Tag Archives: maternal urinary fluoride

More expert comments on the Canadian fluoride-IQ paper

The Green et al (2019) fluoride/IQ is certainly controversial – as would be expected from its subject (see If at first you don’t succeed . . . statistical manipulation might help and Politics of science – making a silk purse out of a sow’s ear). Anti-fluoride campaigners have been actively promoting it as the best thing since sliced bread. But it has not received the same glorification from most experts.

The UK Science Media Centre published a list of reactions from experts (see expert reaction to study looking at maternal exposure to fluoride and IQ in children) and they are worth reading. Also, there are comments from Dr F. Perry Wilson presented in the video above.

Wilson raises some very valid criticisms, a few of which (such as the weakness of the reported relationship) I have dealt with. He also brings attention to how even that weak relationship appears to be strongly affected by extreme values (particularly the few high values for maternal urinary fluoride).

He says:

But as you can see from the scatter plot, the effect was really small—about 1.5 IQ points for moving between the 25th and 75th percentiles of urinary fluoride.”

This is from the data presented in the paper’s Table 2. This low value was not really discussed by the authors who instead promoted an effect of 4.5 IQ points using data covering the whole range, including the unrealistically high urinary F values.

I have already commented in the previous articles on how weak the child IQ – maternal Urinary Fluoride relationship is and how it has no predictive value (see If at first you don’t succeed . . . statistical manipulation might help and Politics of science – making a silk purse out of a sow’s ear). Also, as the mean IQ values for all children and separately for boys and girls are not affected by the residence of mothers in fluoridated and unfluoridated areas it is likely that even this weak relationship is anomalous.

However to return to Dr F. Perry  I have reproduced the transcript of his talk below as he does make a number of valid points worth considering.


Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I’m Dr F. Perry Wilson.

Usually, as studies come across my desk, I say, “Oh, that one is interesting” and dig in to see if it’s worth spending a few minutes of your time on. This week, I saw this study appearing in JAMA Pediatrics and just thought, “Oh no.”

This is one of those studies that I just knew would blow up, and probably for the wrong reasons.

Despite robust evidence that fluoridation of water reduces the incidence of cavities in kids, it has long been a bugaboo of conspiracy buffs, ranging from General Jack D. Ripper to Alex Jones.

No one ever seems to complain about chlorinating water, but whatever.

In any case, the argument that fluoridation is a secret communist plot has never held water, but several prior medical studies have documented a link, however small, between fluoride exposure and lower IQ in children. But all of those prior studies were flawed in one way or another, most often because the exposure was orders of magnitude higher than what is seen in the fluoridated water supply.

Enter JAMA Pediatrics, with what is really the best study to date of the effect of fluoride on IQ. Five hundred and twelve mother-child pairs from Canada were recruited during pregnancy and followed until the kids were around 3-4 years of age. At three points during pregnancy, the moms had their urinary fluoride concentrations measured. These measurements were averaged, and the researchers report that moms with higher levels had kids with lower IQs.

This held up even after adjusting for city, maternal education, race, child sex, and a score that measures the quality of the home environment.

Yikes, right? Is fluoridation causing a process of “dumbening”? Is “dumbening” even a word?

Hold up. It’s caveat time.

First, this was not a randomized trial. No one was giving these moms fluoride or regulating what they drank, so confounders could be a major issue. I’m particularly worried about socioeconomic factors that may be linked to fluoridated water consumption and also children’s IQ.

But there’s potentially a bigger problem. The plausible mechanism for neurotoxicity of fluoride in utero is that blood fluoride crosses the placenta and gets into the fetus’ developing brain. Like this.


But blood fluoride wasn’t measured. Urine fluoride was. Now, as a nephrologist, this piques my interest because urine fluoride is not a perfect proxy for blood fluoride.


The authors know this. They realize, for example, that more dilute urine will have a lower fluoride concentration, and they “correct” this problem by dividing urinary fluoride by urine specific gravity.


But this introduces a new variable. Assuming that fluoride has no effect on a child’s IQ, you could get results that look like this if moms with more dilute urine tend to have kids with lower IQs.

But wait, there’s more. Fluoride is freely filtered at the glomerulus, but it is reabsorbed in the renal tubules. This is a pH-dependent process,[2] with more reabsorption occurring when the pH is lower. That means that women with higher urinary pH (due to a more vegetarian diet or just prolonged fasting) will, on average, have higher urinary fluoride levels.


Another confounder, this one unaccounted for.

Does the presence of possible confounders invalidate the study? Of course not, but these factors remind us to interpret results like this very carefully, especially when the documented benefits of fluoridation rest on much firmer scientific footing than the possible harms.

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Politics of science – making a silk purse out of a sow’s ear

Anti-fluoride activists have some wealthy backers – they are erecting billboards misrepresenting the Canadian study on many New Zealand cities – and local authorities are ordering their removal because of their scaremongering.

Many New Zealanders are concerned at the scaremongering by anti-Fluoride activists lately. Media commenters have criticised misleading advertisements placed in national and local newspapers by Fluoride Free New Zealand (FFNZ). And local authorities have ordered some of the billboards erected by FFNZ to be taken down because of their scaremongering (see Anti-fluoride billboard removed).

A misleading advertisement anti-fluoride activists are inserting in many New Zeland newspapers. Media commentators believe newspapers must allow space for the experts to present the true science listen to Gavin Ellis, Nine to Noon, Sept. 3).

I can fully understand anti-fluoride activists taking advantage of current interest in the recently published Canadian fluoride/IQ study (see If at first you don’t succeed . . . statistical manipulation might help). They are, after all, an advocacy group, well known for their misrepresentation of the science, and they have rich backers in the alternative health industry (see Big business funding of anti-science propaganda on health and Anti-fluoridationists go to Supreme Court – who is paying for this?) to finance this expensive advertising.

As always its a matter of “Reader Beware.”  In this day and age readers are well-advised to take what they see on billboards and in newspapers (particular advertisements) with large dollops of salt.

“Sexy” science

But what disturbs me is the role the personal ambition of scientists and institutional advocacy, the politics of science, has played in this unfortunate misrepresentation and advocacy of the Canadian study.

This is not an isolated case. Scientific researchers with any experience know of many examples where individual scientists have misrepresented or exaggerated their findings because of personal ambition and institutes have gone along with this to obtain kudos (and money). We all know of young scientists who have behaved in this way, effectively promoting their poor science, risen through the ranks and, before long, exited research to take high-paying roles in science administration. More honest researchers are often scathingly critical of such ambition – especially as we often have to put up with these people manipulating funding and distorting scientific directions when they later become administrators. At the same time, we respect the honest researchers who often plod away, making slow but real progress, but not seeking, or getting, full public recognition for their work – because it is not “sexy” enough.

Yes, I like most researchers, have experienced administrators demanding that we make our research more “sexy.” These same administrators have never expressed the desire we make out research more honest, more professional or more effective (except in terms of winning publicity and unthinking funds).

Relying on “authority” statements while ignoring real data

Interestingly, in this current round of scaremongering the anti-fluoride activists do not reproduce data from the studies. There are no graphs, for example. Perhaps the real-life data is so scattered it would expose their claims of specific values of harm as fantasy.

According to an FFNZ post, the IQ of children in this study would have dropped by 4.5 points, from 114.1 where mother’s urinary F concentration (MUF) was 0 mg/L to 109.6 when the MUF was 1 mg/L. But look at the figure below. Very few of the data points near a MUF of 1 mg/L are actually near 109.6. They vary from about 75 to 125! No wonder they do not reproduce the figure from the paper to support their claim.

Instead, they rely on the approach of quoting the statements of “authorities,” some of the authors and others who have commented favorably on the research.

Yes, the authors did state they had found an association (for boys) with a best-fit line (the blue line above) showing an IQ decline of 4.49 points for an increase in MUF of 1 mg/L. But clearly this is meaningless when the very high scatter of the data is considered – it has no predictive value. This is because the claimed IQ reduction represents only the best fit line, the very weak association of IQ with MUF they reported. An association so weak that it refers only to 1.3% of the data (see If at first you don’t succeed . . . statistical manipulation might help).

OK, perhaps I can be accused of ignoring the stated variability of the reported relationship (although so have the anti-fluoride campaigners). Green et al (2019) described the relationship in the abstract of their paper this way:

“A 1 mg/L increase in MUFSG was associated with a 4.49 point lower IQ score (95% CI, -8.38 to -0.60) in boys.”

As a predictor that is saying that 95% of IQ values for boys at a MUF of about 1 mg/L should be in the range 105.7 to 113.5. Again, simply not true (look at the figure above). In fact, this relationship refers only to the best fit line and the blue zone in the figure above indicates where this line could go 95% of the time.

So this “authority” statement about the reported relationship is simply of no practical value as it applies to only 1.3% of the data. It is meaningless and it’s irresponsible for the authors and other “authority” spokespeople to refer to this relationship in the way they have without mentioning how weak it is.

The “authority” statements and those of the authors themselves are doubly worse because they ignore the fact that there is no statistically significant difference for the IQs of all children and separately the boys and girls, for mothers who lived in fluoridated and unfluoridated areas during their pregnancy. The data showing this is in Table 1 of the paper (and presented below) so it is strange that the authors did not discuss this in their paper at all.

Mean IQ of children whose mothers drank fluoridated or unfluoridated water during pregnancy (SD =  11.9 – 14.7)

Nonfluoridated Fluoridated
All children 108.07 108.21
Boys 106.31 104.78
Girls 109.86 111.47

Shameless advocacy by scientists and institutions

Scientists are only human and it’s perhaps not surprising that authors of these and similar studies will exaggerate the importance of their finding and remain silent about deficiencies in their studies. After all, self-promotion of this sort, especially if it gets widespread industry and public attention, can only be good for their careers.

One of the authors, Cristine Till is reported as saying:

“At a population level [4.5 IQ points, SC], that’s a big shift. That translates to millions of IQ levels lost” [reported by CNN]

And:

“We would feel an impact of this magnitude at a population level because you would have millions of more children falling in the range of intellectual disability, or an IQ of under 70, and that many fewer kids in the gifted range…We recommend that women reduce their fluoride intake during pregnancy.” [Reported by NPR]

And:

“Four and a half IQ points is of substantial societal and economic concern…We’re talking a magnitude that’s comparable to what we’re talking about when we talk about lead exposure. You would have millions of more children falling into the range of intellectual disability with IQ scores of less than 70, and that many fewer kids in the gifted range.” [Reported by WebMD]

Looking at the graph we can clearly see that at the population levels there are not these huge losses in IQ. She omits the fact that the relationship they report is extremely weak. Her statement is misleading – but she no doubt feels its good for her career. She also omits the fact shown by their own Table 1 that there is no difference in IQ fo children whose mothers lived in fluoridated or unfluodiated areas.

And then we get promotion of these misrepresentations by other scientists – apparently independent of the authors but a closer look shows them to be linked.

This from  Phillipe Grandjean:

“This is an excellent study,”  . . . CDC has to come out and look at the risk-benefit ratio again, because they can’t continue relying on studies that were carried out decades ago.” (Reported by Washington Post]

Grandjean frequently makes these sort of comments on studies which can be interpreted as supporting anti-fluoride positions. He is even a bit of a go-to spokesperson for the Fluoride Action Network (FAN) and his bias is clear, despite his professional standing. As the chief editor for Environmental Health he would not allow my critique of the Malin & Till (2015) ADHD study to be considered for publication (see Fluoridation not associated with ADHD – a myth put to rest). My critique was later reviewed and accepted by a different journal but ethically it should have been published by the journal which published the original Malin & Till (2015) paper.

Grandjean was one of the people I commented on in my articles about the poor peer review of the Malin & Till paper (see Poor peer-review – a case study and Poor peer review – and its consequences). So was David Bellinger – a subeditor who dealt with the Malin & Till (2105) paper. Bellinger, coincidentally, wrote a supportive opinion piece on the Green et al (2019) paper in the issue of JAMA  Pediatrics which published the Green et al paper.

It amazes me sometimes how incestuous journal editors, paper authors and peer reviewers cna be.

Don’t get me wrong. there was also quite a widespread criticism of the Green et al (2019) paper in the scientific community. Hopefully, some of these critics will contribute critiques of the paper to the journal. Also, hopefully the journal editor will allow these critiques to be published (although, as I point out in If at first you don’t succeed . . . statistical manipulation might help the editor seems only to be welcoming debate on these findings if it is in the public media).

The point, of course, is that activist anti-fluoride organisations like FAN and FFNZ never quote those critics. they simply quote the apparently “authoritative” figures who have praised the paper or promoted the misinformation described above. Thes misleading quotes from authors, institutes and “authority” supporters are simply mana from heaven to the FAN and FFNZ activists.

Dangers of science politics allied with ideologically-motivated advocacy

Problems with the politics of science occur all the time. That is why I always suggest readers should look at papers, even those in the most reputable journal, critically and intelligently. Importantly, one should look at the actual data where possible to check that it is portrayed properly in the discussion, conclusions and abstract. Otherwise, it is easy to be misled by ambitious authors, public relations press releases from institutions and “independent” scientific commenters.

Also, only the most naive reader accepts information in news articles and adverts as necessary gospel truth. The sensible reader approaches the media and advertising critically.

However, in this case, I think people have a right to be far more concerned about the misinformation – both that presented by authors, their institutes and their colleagues, and the way it is presented to us by the media and advertising. This is because the worst sort of fear-mongering is involved – playing on our love for our children and inherent wishes to do anything to protect them.

So I support the concern expressed by people in the media, the suggestion that such advertising should be accompanied by more informed articles, and the actions of local authorities in ordering the offending billboards be taken down. I passionately believe in free speech and defend the rights of even those I think wrong to partake of this – to express their opinions. But when the wellbeing and health of children and their parents are compromised by that free speech I think there is a case for it to be limited.

After all, there are other avenues, especially one which enable claims to be challenged properly, where that free speech can continue without creating harm.

Science reporters should be more responsible

I can’t finish without airing a concern I have about science reporters. In a sense, they are in a privileged position because the subjects they deal are credible because science is involved. Science does have a reputation for getting to the truth and being objective.

Privilege is also conferred on these reporters because they continually cite and quote experts – people of “authority” because of their education and scientific positions.

But surely an experienced science reporter is aware of the problems of politics in science – the role of ambition and search for fame which can lead to misrepresentations or at least over-glorification of the subjects being reported by the researchers involved. They must also surely be aware that different schools of thought within the scientific community can lead to biased presentations.

It’s not good enough for science reporters to simply quote authors and biased researchers. Surely they have an obligation to do some checking on the credibility of the claims being made. Why not read the full papers rather than rely on an abstract or an author’s claim? Further, and more importantly, why not cast a critical eye over the evidence reported in the paper and the data if it is there? Surely most science reports have some scientific and statistical skills.

I realise reporters have deadlines. In this case, some of the “authorities” commenting on the paper had been given prior access – a bit unfair for other reporters. It is tempting to go with what one has and not delay an article by indulging in critical analysis. But reporters should also think responsibly. Misinformation, in this case, is being used to promote dangerous scaremongering. That scaremongering should not be assisted by negligent reporting.

I am saddened that hardly any reporters quote the important information from the paper – that presented in the paper’s Table one and the table above. Differences in IQ of children whose mothers lived in fluoridated or unfluoridated areas are not different – or more correctly the differences (changes of +0.14 points for all children, -1.53 points for boys and + 1.61 points for girls when fluoridation is involved) are not statistically significant.  OK, the authors and their promoters were silent about that data – but a good reporter should have picked it up.

On the other hand, most science reporters ignored the actual data and went with the quotes. So instead of the data in the table above a misleading IQ change of 4.5 points for boys was presented as the main message. With absolutely no evaluation of how weak the relationship used to obtain that figure is.

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Maternal urinary fluoride/IQ study – an update

Model of a fetus in the womb. Photo credit: CP PHOTO/ Alliance Atlantis/ HO) 

The maternal urinary fluoride/IQ study  (Bashash et al., 2017) continues to get attention – but mainly from anti-fluoride organisations. The scientific community will evaluate the published report after giving it due consideration and there have already been criticisms. But anti-fluoride campaigners consider it the best thing since sliced bread. The Fluoride Action Network (FAN) describes it as “a cannon shot across the bow of the 80 year old practice of artificial fluoridation” and Fluoride Free NZ insist that it “must spell an end to fluoridation in New Zealand.”

We expect confirmation bias from the anti-fluoride organisations. But the misrepresentations in the propaganda from these organisations are of more concern because they are blatantly meant to scaremonger.

Misrepresentation by anti-fluoride organisations

These people have worked hard to stress the respectability of the authors of the Bashash et al., (2017) paper and claim the study is impeccable. They are not interested in a critical analysis of the data and the conclusions. And they are completely silent about the evidence from the study showing no association of children’s urinary fluoride levels and IQ – normally they are quick to criticise authors reporting such a lack of association.

But this time as well as their normal misrepresentations they have actually manipulated a figure from the paper. I wonder what copyright law would say about this.

I provided the relevant figures from the paper my earlier article (see   Fluoride, pregnancy and the IQ of offspring) and commented on the large amount of scatter in the data.  This scatter should be a warning to any sensible reader – so FAN simply overcomes that problem by deleting the data points in their presentation of the figure.

Here is the original Figure 2 and the FAN misrepresentation of it:

Notice 2 things:

  1. The original figure showed the data for GCI – general cognitive index. It is not IQ and not presented as IQ in the original paper. But it is a measure  of “verbal, perceptual performance, quantitative, memory, and motor abilities of preschool-aged children.” Perhaps a fine point and FAN may be excused for inserting the more popularly understood term IQ. Or perhaps they decided not to use the real figure for IQ (Figure 3A) because it implied no effect at normal urinary fluoride levels (see figure 3A in Fluoride, pregnancy and the IQ of offspring);
  2. FAN removed all the data points in their presentation of the figure. I am sure FAN would argue this was to “simplify” the figure. But in doing so they have removed what is the most important information in Figure 2 – the wide scatter of the data points. That scatter suggests that even though the reported association is “statistically significant” it explains very little of the observed variation and is therefore not important (and may not even be real).

Association of maternal urinary F with child IQ poor and probably misleading

In Fluoride, pregnancy and the IQ of offspring I estimated that “the reported relationships with maternal urinary fluoride could explain no more than a few percent of the variation in the data.” Purely an estimation because I did not have the data to analyse myself and the authors did not give the relevant statistical information.

I have since used a plot digitiser programme to extract the data for these figures and performed my own statistical analysis.

These are the results:

For Figure 2:

Bashash-fig2

Yes, a “statistically significant” relationship (p = 0.002) but it explains only 3.3% of the variation in GCI (R-squared = 0.033)

For Figure 3A:

Bashash-figs3A

Again, “statistically significant” (p = 0.006) but explaining only 3.6% of the variation in IQ (R-squared = 0.0357).

So my estimate was pretty good. And my evaluation is valid:

“In this case, I would expect that other risk-modifying factors that explain the variation more completely could be found. And if these were included in the multiple regressions there may not be any observable relationship with urinary fluoride.”

Considering that this work was unable to explain about 97% of the variation in CGI and IQ I really question its publication. Certainly, scientific evaluations will conclude that this paper should not have any influence on policymakers.

It’s a pity that with all the data the authors had they did not seek out, or properly evaluate, other possible risk-modifying factors.

Other work by group showing no association ignored

Strangely, the Bashash et al., (2017) paper did not include relevant IQ information from the PhD thesis of one of their team Deena B. Thomas. This is her thesis citation:

Thomas, D. B. (2014). Fluoride exposure during pregnancy and its effects on childhood neurobehavior: a study among mother-child pairs from Mexico City, Mexico. PhD thesis, University of Michigan.

It can be downloaded from the full-text link.

The data in chapter 2 of this thesis – Urinary and Plasma Fluoride Levels During Pregnancy and Determinants of Exposure Among Pregnant Women from Mexico City, Mexico – was published. The citation is:

Thomas, D. B., Basu, N., Martinez-Mier, E. A., Sánchez, B. N., Zhang, Z., Liu, Y., … Téllez-Rojo, M. M. (2016). Urinary and plasma fluoride levels in pregnant women from Mexico City. Environmental Research, 150, 489–495.

Bashash et al., (2017) did reference this paper – after all, it dealt with the data they used for estimating fluoride exposure. But they did not reference the thesis itself – and two other chapters in that thesis are directly relevant to the relationship of fluoride exposure to child IQ.

Chapter 3 – Prenatal fluoride exposure and neurobehavior: a prospective study – is directly relevant except that where Bashash et al., (2017) reported data for the children when 4 years old and 6-12 years old Thomas reported data for child neurobehavioral outcomes at ages 1, 2 and 3.

She concluded:

“that maternal intake of fluoride during pregnancy does not have a strong impact on offspring cognitive development in the first three years of life.”

OK – perhaps the difference is purely due to age. But surely it is part of the picture and should at least been mention in the Bashash et al., (2017) discussion.

Chapter 4 – Concurrent Fluoride and Total WASI in 6-15 year old children from Mexico City, Mexico – is also directly relevant because Bashash et al., (2017) did include that data in their paper. They concluded that:

“there was not a clear, statistically significant association between contemporaneous children’s urinary fluoride (CUFsg) and IQ either unadjusted
or adjusting for MUFcr.”

This differs a little from the findings in Thomas’s thesis:

“In the overall population, urinary fluoride appears to have no significant impact on total WASI scores (β =1.32, p=0.33), but this association changes once the models are separated by male and female children. Male children showed a significantly positive trend (β=3.81, p=0.05), and females showing a negative trend that was not significant (β= -1.57, p=0.39).” [WASI score is a measure of IQ]

And she wrote:

“analysis suggests concurrent urinary fluoride exposure has a strong positive impact on cognitive development among males aged 6-15 years.”

She concludes:

“These results were surprising in that they show opposite trends to what has been reported in the literature so, more studies with similar reliable methodology, which account for plasma fluoride, diurnal variations in urinary fluoride and children’s SES, are needed. If these results are substantiated, different fluoride interventions may be needed for male children versus female
children.”

I would have thought these findings and conclusions were worthy of discussion by Bashash et al., (2017). It’s not as if the authors were unaware of their colleague’s findings.

Maybe internal politics are involved. but that does not justify the omission.

Conclusion

The anti-fluoride people, and particularly FAN, are misrepresenting the study and have manipulated a figure to hide information in an unethical way. The data presented in the Bashash et al., (2017) study shows maternal urinary fluoride can only explain 3 – 4 % of the variation in General Cognitive Index and IQ of the children. The inclusion of a more viable risk-modifying factor would probably remove even that small amount explanation.  Bashash et al., (2017) also neglected to discuss relevant information from a colleague which contradicted their conclusions.

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Fluoride, pregnancy and the IQ of offspring

Anti-fluoride campaigners don’t agree. Image credit:Dental Care Tips for Mom and Baby” presentation

What’s the story about this new IQ-fluoride study? The one that claims fluoride intake by pregnant women could endanger their children’s IQ?

Whatever the truth, it has certainly got the anti-fluoride activists going. Mary O’Brien Byrne, leader of the local anti-fluoride group is even suggesting people check if their mothers lived in fluoridated areas. And they are busy promoting the newspaper articles on this. For example Fluoride exposure in utero linked to lower IQ in kids, study saysChildren’s IQ could be lowered by mothers drinking tap water while pregnant, and Higher levels of fluoride in urine linked to lower IQ scores in children.

Best not rely on those media reports, though – you know how unreliable they can be. The original paper is available – this is the citation:

Bashash, M., Thomas, D., Hu, H., Martinez-mier, E. A., Sanchez, B. N., Basu, N., … Hernández-avila, M. (2016). Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6 – 12 Years of Age in Mexico. Environmental Health Perspectives, 1, 1–12.

And here is a link to the full text. Download it and see what sense you make of it. I warn you it is a difficult paper to read.  A lot of information is lacking and the information that is included is hard to find. The statistical analysis is incomplete.

A new twist on the tired old fluoride/IQ story

Basically, it is the old drinking water fluoride causes lowering of IQ story. This time it relates to a supposed association of fluoride intake by pregnant mothers with cognitive deficits in their children. Interesting, only one other similar study (involving fluoride exposure while pregnant) has been reported – in January this year, and also in Mexico. I wrote about that study of Valdez Jiménez et al., (2017), In utero exposure to fluoride and cognitive development delay in infants,  in the article Premature births a factor in cognitive deficits observed in areas of endemic fluorosis?

Briefly, the Valdez Jiménez et al., (2017) study was from Mexican areas of endemic fluorosis with very high fluoride concentrations in drinking water so the results are not applicable to areas where community water fluoridation is used. However, the high incidence of premature births, and low birthweights for the children, for mothers with high urinary fluoride levels does suggest that problems of birth in areas of endemic fluorosis could provide a biological mechanism to explain the IQ deficits. Rather than a direct chemical toxicity mechanism.

What about the Bashash, et al. (2017) paper?

Generally, the paper concludes that “higher prenatal fluoride exposure . . . .was associated with lower scores on tests of cognitive function in the offspring.”

So here are some concerns I have about the paper

1: An association is not evidence of, or proof for, causation. Yes, that is the normal and obvious qualification for such studies and authors tend to repeat it – even if they might still attempt to argue the case that it is evidence. A lot of confirmation bias goes on with these sort of correlational studies.

2: The information about the mothers is scant. My first question, given it was Mexico, was did they come from areas of endemic fluorosis? The women were recruited from three hospitals in Mexico city but this says nothing about their current or former residential areas. No information on drinking water fluoride is presented nor any biological assessment, such as dental fluorosis, given which could help estimate the role of endemic fluorosis.

3: Assessment of fluoride exposure relied completely on urine fluoride concentration measurements. With between one and three samples for each mother-child pair! (Of the total sampled there was only one sample for 217, two for 224 and three for 71 mothers). I believe that is completely inadequate for estimating exposure – especially as fluoride levels in urine vary markedly during the day and with diet. Besides the extremely low sample numbers,  the World Health Organisation has warned that while urinary fluoride can be useful for monitoring populations “Urinary fluoride excretion is not suitable for predicting fluoride intake for individuals.”  (see Contemporary biological markers of exposure to fluoride). They further warn that 24 hr collection is preferred to the spot sampling used in this study.

4: The statistical information presented is confusing – and insufficient to estimate how relevant the reported statistically significant associations are. I believe the best idea of the data can be gleaned from the following figures presented in the paper.

Figure 2 displays the data and association of maternal urinary fluoride (MUFcr) with a general cognitive index (CGI) for the 4 yr old offspring.

Figure 3A displays the data and association of maternal urinary fluoride (MUFcr) with IQ of the offspring at age 6 -12.

While linear regression analysis showed statistically significant associations of the CGI and IQ of offspring’s with maternal urinary fluoride levels the large scatter indicates these associations will explain only a small part of the variations observed. In such situations, reliance on p values can be misleading. As a reader, I would be more interested in the R2 values which indicate the amount of variation explained by the association.

I estimate the reported relationships with maternal urinary fluoride could explain no more than a few percent of the variation in the data. In this case, I would expect that other risk-modifying factors that explain the variation more completely could be found. And if these were included in the multiple regressions there may not be any observable relationship with urinary fluoride.

I discussed this issue more fully in my article Fluoridation not associated with ADHD – a myth put to rest which showed that a published relationship of ADHD with fluoridation extent disappeared completely when altitude was included as a risk-modifying factor. And that relationship showed less scatter of the data points than in the figures above.

5: The absence of any association of child IQ to child urine fluoride was also reported in this paper. This conflicts with other researchers working in areas of endemic fluorosis who have reported such associations. It could be that the urine fluoride measurements used in the present study were not suitable. But I am picking that the anti-fluoride campaigners will be very silent about that information, given the importance they give to other studies showing a relationship in their propaganda.

Conclusions

it is a very unsatisfying paper. I couldn’t determine if areas of endemic fluorosis were implicated – as they were for the Valdez Jiménez et al., (2017) study. Urinary fluoride is an inadequate measure of fluoride exposure – especially for individuals and spot samples – and its variability does not allow comparison with other studies and other regions. I couldn’t evaluate if the reported results were relevant to New Zealand which does not have any endemic fluorosis.

Finally, I believe aspects of the statistical analysis were inadequate. But on the positive side, I am pleased the authors did display the actual data in their figures. The information in those figures forced me to conclude that maternal urinary fluoride may not have the influence the authors suggest. If it does have an influence its contribution can only be minor and other more important risk-modifying factors will be involved.

Mind you – I am sure anti-fluoride campaigners will see it differently. They are currently heavily promoting the study and anti-fluoride guru Paul Connett sees it as the best thing since sliced bread. He has gone on record to say this means the end of community water fluoridation!

Update

I think the anti-fluoride people are aware of weaknesses in this study. The local Fluyodie Free NZ has put out a press release including a figure which they have doctored to remove the data points which show how little variation is explained. Compare their figure with the Fiugure 2 above.

Fluoride Free NZ doctors figure from paper to hide the scatter in data points showing how little of the variability the relationship explains

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